Modern Physics Test 1 Online MCQs

1. The orbit radius of the electron in the hydrogen atoms changes from r to 4 r. The energy of the orbital electron will change from E to:

2. The radius of Bohr’s first orbit is r. What is the radius of the first orbit in the singly ionized helium atom?

3. In an atom, the two electrons revolve around the nucleus. What is the ratio of their time periods in the first excited state and the ground state.

4. Who proposed that the orbits of the electron in the atom are elliptical?

5. The ionization of energy hydrogen atom is 13.6 eV. Hydrogen atoms in the ground state are excited by monochromatic radiation of photon energy 12.1 eV. The spectral lines emitted by hydrogen atom according to Bohr’s theory will be:

6. A photo sensitive metal is not emitting photoelectrons when irradiated. It will do so when threshold is crossed. To cross the threshold we need to increase:

7. The energy difference between the first two levels of hydrogen atom is 10.2 eV. For another element of atomic number 20, this will be:

8. The orbital electron of the hydrogen atom jumps from the ground state to a higher energy state and its orbital velocity is reduced to one third of its initial value. If the radius of the orbit in the ground state is r, then what is the radius of the new orbit?

9. Ionization of energy hydrogen atom in the ground state is E. What is the ionization energy in the L⁺⁺ atom in the 2^nd excited state?

10. Which of the following is not property of the photons?

11. The study of photoelectric effect is useful in understanding:

12. The maximum energy of the electrons released in photocell is independent of:

13. The ionization potential of hydrogen atom is 13.6 V. How much energy need to be supplied to ionize the hydrogen atom in the first excited state?

14. When a photon collides with an electron which of the following characteristic of the photons increases?

15. Suppose the element with principal quantum number n > 4 where not allowed in nature, what would have been the total number of elements in nature?

16. A photosensitive material would emit electrons if excited by photons beyond a threshold. To cross the threshold you would increase:

17. The orbital velocity of the electron in the ground state of hydrogen atom is v. What will be its orbital velocity when excited to the energy state – 1.51 eV?

18. Which of the following makes use of photoelectric effect?